Reverse Polarity Outlets
A common defect found when inspecting the electrical system in a home are reverse polarity outlets. When found, it's typically a sign of a non-professional repairs completed by a homeowner or an inexperienced handyman.
Reverse polarity outlets occur when the hot (black) and neutral (white) wires are flipped. In this situation, the wires are connected to the incorrect terminals on the outlet, or improperly connected at an upstream connection. Reverse polarity is an electric shock hazard, but typically it's an easy repair.
Want to know if your outlets are reverse polarity? A $10 electrical tester used on a properly grounded 3-prong outlet can help identify reverse polarity outlets, and other wiring defects, in your home. In the picture above, you can see an example of how a properly grounded electrical outlet tester can identify a reverse polarity outlet. Occasionally, these home electrical testers are not accurate (e.g., non-grounded 3-prong outlets), but they are a great starting point to determine unsafe wiring conditions within your home.
Understanding Hot and Neutral Wiring
On a standard outlet (duplex outlet) you would expect to find in your home, there are 2 wires that carry electricity. The white or neutral wire is connected to the earth and is the grounded conductor. This is the largest slot on an outlet and has silver screws to connect the wires to. The non-grounded conductor, or hot wire, is not connected to the earth, and can be any color other than white or green. In a standard home these will be black, but you may also see red or blue wiring. The smaller slot on an outlet is for the hot non-grounded conductor and has gold screws to connect the wiring.
(There are exceptions to the silver and gold screws, such as newer outlets designed for Aluminum wiring, so always read the wiring diagram prior to installation.)
Since the hot wire completes the circuit when it encounters the earth, when you touch a hot wire and are in contact with earth, which is a large percentage of time, you complete the circuit and get electrically shocked.
Typical Outlet Wiring
Here is an example of typical wiring for an outlet. Always check the wiring diagram for your equipment prior to installation.
What would make this example 100% would have been if the hot and neutral wiring were both connected to the lower screws.
Polarized Plugs and Outlets
As previously discussed, the slots on the outlets are different sizes. You will also see plugs with different sized prongs. This is to ensure proper polarization to electronics when they are connected to the electrical system.
Real World Example of How Reverse Polarity Can Cause Electrotion
In a table lamp fixture, the metal socket that you screw the bulb into is connected to the neutral wiring. When the outlet you are using is wired correctly, if you accidently touch the housing, nothing happens. When the light is plugged into a reverse polarity outlet, the housing is energized, and if you touch the housing and complete the circuit, the result is an electrical shock or electrocution.
First and foremost, electrical repairs should only be completed by people familiar and comfortable with how electricity and electrical systems work. If in doubt, call an electrician.
Depending on the extent of the wiring issues, fixing reverse polarity outlets may be as simple as flipping the wires at the outlet. If the wires are correctly attached to the outlet, the problem lies somewhere upstream, and a more diagnostic search will need to take place to determine where the defect begins, and what repairs will be needed. There are lots or resources and education materials available to reference to ensure you complete any repairs safely and accurately.